This invention relates to the production of smooth-edged metal parts, and, more particularly, to the production of smooth-edged metal parts having complex perimeter configurations, such as gears and sprockets.
Numerous methods exist today for producing metal parts. One such method is stamping, by which stock material, typically a metal sheet, is fed into a punch press. The punch press, typically via some sort of die and punch arrangement (stamping die), stamps out parts, which can be in the form of xe2x80x9cblanks.xe2x80x9d A blank, an example of which is shown in FIG. 2, is typically a right cylinder solid having a desired perimeter outline and the same thickness as the original metal stock. For example, conventional round washers, which have a simple circular perimeter, are usually manufactured via a stamping process in conjunction with an integral piercing process for providing a center hole. Blanks may be used as parts in and of themselves, or may be used as intermediate articles of manufacture for producing parts from the blanks.
The production of blanks, or more complex parts such as stamped gears or sprockets, is typically carried out either by a conventional stamping process or by a xe2x80x9cfine blankingxe2x80x9d process.
In the conventional stamping process, the cooperating punch and die produce an initial shearing action after which the blank is severed from the surrounding stock material by fracturing. This results in the stamped gears or blanks having a disadvantageous feature known in the art as xe2x80x9cdie break.xe2x80x9d A ridge, known as xe2x80x9cshear,xe2x80x9d extends around the edge of the stamped blank and divides the portion of the blank that has sheared from the portion that has fractured. The fractured portion is the xe2x80x9cdie break,xe2x80x9d and is rough and granular in nature. As the thickness of the stock from which the blank is produced increases, so does the problem of die break.
In order to obtain a smooth-edged piece (that is, a blank or gear having a vertical side edge without shear), a secondary operation called xe2x80x9cshavingxe2x80x9d is, in traditional prior art, required. Besides being an additional manufacturing step, shaving is disadvantageous in that the amount of material being removed is very small, e.g. approximately 0.010 inch, and is typically in the form of metal slivers. These small pieces may be difficult to remove from the manufacturing machine. Another problem with shaving is that if the metal has a yield strength exceeding 60,000 PSI, small tears may form in the side of the blank. In a gear, these tears (which develop in the gear teeth) may make the gear unacceptable for use.
Another disadvantage in producing gears using conventional stamping methods is that the gear teeth may be deformed on the die-side of the gear blank. This deformation is called xe2x80x9cdie rollxe2x80x9d or xe2x80x9cpull downxe2x80x9d, and can exceed 60% of the material thickness.
The problem of die break is largely averted by using the fine blanking process. One such fine blanking machine is disclosed in U.S. Pat. No. 3,570,343 to Wolnosky et al.
Fine blanking is an extrusion process carried out by clamping the blank and stock material in such a manner as to prevent die break when the extrusion punch and die perform the blanking operation. Although fine blanking eliminates the die break portion of the blank, it suffers from substantial drawbacks.
Two of the most serious problems with fine blanking are the need to provide a special press and the slow operational speed of such a press. Typically, the special press is a triple action punch press which operates to provide three required forces: shear pressure, xe2x80x9cvee ringxe2x80x9d pressure, and counter pressure. The required special press is particularly expensive and must be extremely robust to provide sufficient support to absorb reaction, sudden pressures, and vibration.
Additionally, fine blanking presses must securely clamp both the blank and the stock material from which the blank is stamped. To this end, it has been necessary to provide a special component feature to encircle the area to be blanked out. That special component conventionally comprises an upstanding pointed ridge which serves to engage and bite into the stock material around the area to be blanked out. The ridge is termed a xe2x80x9cstingerxe2x80x9d and may be embodied in a tooling component known as a blanking die, or may be embodied in a tooling component known as a xe2x80x9cstripper,xe2x80x9d which is utilized to remove the surplus stock material after the stamping or blank has been removed. In either event, the precise location of the stinger and the need to securely clamp the surplus blank material necessarily results in a press which is intricate, expensive, and cumbersome. Also, the use of a stinger requires sufficient surplus stock material to permit the desired clamping, thereby causing waste.
Furthermore, when it comes to producing tooth forms, for gears or sprockets for example, the fine blanking process is limited. As a general rule, for fine blanking, the tooth thickness at the pitch radius should be equal to 60% of the stock thickness. This may be unacceptable. Also, to prevent die break, the roots and crests of the gear teeth must be radiused, and in cases where tooth width approaches a minimum limitation (typically around 40% of stock thickness), die roll at the tips of the teeth will be considerable.
These limitations regarding gear and sprocket production also apply to the conventional stamping methods, and to the GRIP FLOW(copyright) brand metal stamping apparatus disclosed in U.S. Pat. Nos. 4,267,753 and 4,951,537 issued to the present inventor. As such, it has been necessary to employ secondary, additional operations to produce acceptable gear teeth, e.g. gear hobbing, gear cutting, gear broaching, gear grinding, etc. These methods require expensive machines, skilled labor, high maintenance costs, and operate at limited production speeds.
Wherefore, it is an object of the present invention to overcome the aforementioned problems and drawbacks associated with the prior art designs.
Another object of the invention is to provide a stamping die that produces metal parts that are extremely true to measurement and that have cut surfaces equal in quality to those which can be machined.
Yet another object of the present invention is to provide a stamping die capable of manufacturing metal parts having complex perimeter edge configurations, such as gears, sprockets, and gear racks.
Another object of the invention is to provide a stamping die for producing gears, sprockets, and the like, having straight sided, uniform gear teeth.
Still another object of the present invention is to provide a stamping die that eliminates the need for metal shaving, and that can be configured to reduce mess and stamping die contamination, both of which limit production speed.
To attain these and other objects, the present invention provides a stamping die that produces gears or other parts having quality tooth forms with smooth and straight edges. The parts are preferably made from pre-stamped, smooth edged metal blanks having substantially the same diameter as the parts to be manufactured.
A bottom portion of the stamping die includes a non-moving trim punch whose perimeter shape corresponds to the shape of the desired part. The trim punch extends through a complementary shaped opening provided in a biasable stripper plate, which surrounds the trim punch and is vertically moveable with respect thereto. The stripper plate further includes a recess surrounding the trim punch for aligning the blanks.
An upper portion of the stamping die is precisely aligned and vertically moveable with respect to the lower portion. The upper portion is mounted to the punch press ram. Connected to the underside of the upper portion is a trim die. The trim die has a concentric bore disposed therethrough whose perimeter is also in the shape of the desired part. The trim die bore is aligned with the trim punch, and there is only a minimal radial clearance between the two (i.e. the trim die bore is dimensioned to allow the trim die bore to enter therein with a minimal radial clearance). A downwardly facing edge of the bore perimeter is radiused in diametral cross-section, and forms a trimming or cutting edge. A nest plate is affixed to the underside of the trim die, and has a tapered nest opening that aligns with the trim die bore. The perimeter shape of the opening corresponds to an outer diameter of the blank. A controllably pressure spring biased shedder passes through the bore and opening and extends just beyond the underside of the nest plate. Also, respective piercing features may be provided for facilitating a piercing operation.
The minimal clearance between the trim die bore and the trim punch, is preferably, in the case of a circular blank, a radial clearance of from about 0.0003 inch to about 0.001 inch, for example, for a blank thickness of about 0.125 inch to about 0.375 inch, respectively. This radial clearance may be, typically, no more than about 1% of the stock thickness.
The radiused edge of the die bore, normal to the longitudinal axis of that bore and the edge on the diametral curve of the bore, preferably has a radius of from about 0.005 inch to about 0.025 inch depending on the type and thickness of the stock material.
The opening of the nest plate has a radial clearance from the trim punch, preferably of from about 0.001 inch for a relatively small diameter blank (e.g. 1 inch) to about 0.005 inch for a relatively large diameter blank (e.g. 6 inches),
During operation, a blank is first placed in the recess. The punch press ram subsequently descends, with the underside of the shedder contacting the blank, and the shedder being forced slightly upwards against its spring bias means. The blank is thus sandwiched between the shedder and the trim punch, with the stripper being held clear of the blank by the nest plate. The portion of the blank to be trimmed is thus left unsupported. The punch press ram then moves further downwards, with the trim punch in effect advancing into the bore and the cutting edge of the trim die trimming the blank. The trimmed scrap portions attempt to flow away from the trim punch, but are constrained by the nest plate, whose tapered shape causes the scrap portions to partially flow together, forming a scrap ring around the trim punch.
Once the trimming operation is completed, the punch press ram retracts upwards, and the finished part is ejected from the punch press. Then the stripper, which had been moved downwards upon the action of the downwards traveling nest plate, is raised so as to free the scrap ring from the trim punch.
The present invention relates to a punch and die combination for producing a part from a blank, the combination comprising: a trim die (1) defining a bore (10) with a radiused edge for facilitating metal flow; a cooperating trim punch (5) dimensioned closely to mate with the bore (10); a blank engaging shedder (2) displaceable within the bore (10) for engaging the blank; a stripper (4) encircling the trim punch and displaceable therealong for removing surplus stock after a trim operation; and a nest plate (3) having an aperture for positioning the blank and for preventing material being trimmed from the blank from moving laterally beyond the nest aperture, the nest plate being affixed to one of the stripper and the trim die.
The present invention also relates to a stamping die for producing a part from a blank, the die comprising: a lower portion comprising: a trim punch (5) having a perimeter shape corresponding to a desired perimeter shape of the part; and a stripper plate (4) having an aperture disposed therein complementary in shape to the trim punch perimeter, the stripper plate being aligned with the trim punch and vertically movable with respect thereto such that the trim punch can pass through the aperture; and an upper portion in alignment with the lower portion and vertically movable with respect thereto, the upper portion comprising: an upper die shoe (17); a trim die (1) affixed to the upper die shoe, the trim die having a bore (10) disposed therein, with at least a portion of a lower perimeter edge of the bore being radiused to provide a trimming operation cutting edge, and a perimeter of the bore being complementary in shape to the trim punch; a vertically controllably moveable shedder (2) having a perimeter shape corresponding to the desired perimeter shape of the part, and the shedder passing through the bore (10) and being vertically displaceable with respect to that bore; and a nest plate (3) having a nest aperture disposed therein for positioning the blank and for preventing material being trimmed from the blank from moving laterally beyond the nest aperture, and the nest plate being affixed to an underside of the trim die with the nest aperture being aligned with the bore.
The present invention further relates to a stamping die for producing a part from a blank, the stamping die comprising: a lower portion comprising: a trim punch (5) comprising an at least partially cylindrical body having a flat top surface and a vertical side wall depending from the top surface, the top surface having a perimeter the same as a desired perimeter shape of the part to be manufactured; and a stripper plate (4) vertically movable with respect to the trim punch, the stripper plate having an aperture disposed therein complementary in shape to the perimeter shape of the trim punch and aligned with the trim punch for the trim punch to pass through the aperture; and an upper portion aligned with and vertically movable with respect to the lower portion, the upper portion comprising: an upper die shoe (17); a trim (1) die affixed to the die shoe, and the trim die having a bore disposed therethrough aligned with and complementary in shape to the trim die, and at least a portion of a lower perimeter edge of the bore being radiused for providing a trimming edge; a nest plate (3) having a nest aperture disposed therein for positioning the blank and for preventing material being trimmed from the blank from moving laterally beyond the nest aperture, the aperture having a perimeter shape the same as the blank and the nest plate having the same thickness as the part, and the nest plate being affixed to an underside of the trim die with the nest aperture being in alignment with the bore; and a shedder (2) complementary in shape to the bore and extending down therethrough and through the opening in the nest plate, the shedder being vertically displaceable with respect to the trim die and the nest plate.